A) when a germanium crystal is doped with a impurity containing 3 valence electrons
B) from pure germanium
C) from pure silicon
D) when a germanium crystal are doped with an impurity containing 5-valence of electrons
Correct Answer: D
Solution :
An n-type semiconductor is obtained by carrying out a process of doping, that is, by adding an impurity of valence five electrons to a valence four semiconductor in order to increase the number of free (in this case) negative charge carriers. The purpose of n-type doping is to produce an abundance of mobile or carrier electrons in the material. An atom with five valence electrons such as those from group VA of the periodic table, (e.g., phosphorous, arsenic or antimony) is incorporated in crystals lattice in place of silicon atom then it gives rise to n-type semiconductor.
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